Strike Impact Research Articles

Assessing wind turbine lightning risk using data-driven methodology

This paper presents a methodology to conduct a risk assessment of lightning damage for wind farms using a data-driven methodology. Methods exist to address risks related to fire but this approach goes further to address lightning damage and related impacts to operations and maintenance comprehensively - monetizing the costs of these impacts. The process begins with lightning data analysis and strike rate calculation. Then, the lightning damage data is analyzed to gain insight into the repair cost and impact. Lastly, the process-based cost model takes lightning strike rate and impact data, resulting in risk provision. The paper presents two case studies, one for onshore wind farms and one for offshore wind farms. The relative importance of operations and maintenance costs versus lost revenues due to downtime (liquidated damages) differ between the two cases due to underlying technical drivers (turbine sizes, wind farm performance, lightning prevalence) as well as market drivers (labor costs, electricity prices). Thus, the study demonstrates both the viability of the method in providing monetary estimates of lightning damage costs over the lifteime of a wind farm as well as the importance of site-specific analysis and models to ensure accurate estimation of those costs.

Research on bird strike resistance performance of hollow plates with warren structure

This study initially conducted bird strike tests and numerical simulations on hollow plates with the Warren structure. The plates manifested notable plastic deformation devoid of fracture. The simulated deformations and strain data of the plates closely corresponded with the outcomes of bird strike impact tests, thereby validating the employed bird strike simulation methodology in this study. Subsequently, while maintaining the outer dimensions of the hollow plate constant, an investigation into the structural parameters of the hollow plate was conducted. Correlations between the thickness of the outer panel, thickness of the Warren, angle of the Warren, and the anti-bird-strike performance of the hollow plate structure were established. The research findings offer valuable insights for informing the design of bird strike resistance in engine blades and hollow plates.

Simulating lightning effects on carbon fiber composite shielded with carbon nanotube sheets using numerical methods

The demand for lightweight aircraft structures has shifted from traditional metals like aluminum to composite materials such as carbon fiber reinforced polymers (CFRP) to achieve weight reduction. However, this transition has led to decreased lightning strike protection efficiency due to the dielectric nature of CFRP. To address this problem, two CFRP samples—one unprotected and the other shielded with carbon nanotube (CNT) sheets—were subjected to artificial lightning strike testing. The research employed a coupled thermal-electrical finite element analysis method to investigate the lightning strike's impact and damage mechanisms on both samples. The numerical results closely aligned with published experimental data, validating the simulation. Unprotected CFRP sustained damage through the thickness direction up to 8 composite plies and in-plane direction over a length of 110 mm. In contrast, the sample protected with CNT sheets exhibited damage limited to the surface of the first 4 plies, with in-plane damage reduced to 24 mm. Notably, the damage area in the CFRP protected with CNT sheets showed a substantial 78.1 % reduction compared to the unprotected CFRP sample. This suggests that CNT can enhance the electrical conductivity of CFRP when incorporated between interlayers in both in-plane and thickness directions. The study enhances understanding of CFRP damage behavior and failure modes under lightning strike conditions, emphasizing CNT sheets as an improved and viable lightning strike protection system for aerospace applications, warranting further investigation.

THE IMPACT OF LIGHTNING STRIKE ON HYBRID HIGH VOLTAGE OVERHEAD TRANSMISSION LINE – INSULATED GAS LINE

The electrical network is the set of elements where loads are connected to the generation plants by transmission lines. They can be either overhead or underground cables. A new technology has been introduced to replace these transmission lines with underground cables gas insulated line “GIL”. The latest has many advantages over underground cables and overhead transmission lines, such as low transmission losses, less capacitive load, reliability, personal safety, same operation as overhead lines and negligible electrical aging. GIL can handle much more power than overhead lines due to its large conductive area. GIL is the best for high voltage. In this paper, the simulation of lightning strike effects on a 400 kV hybrid transmission line located in the Wilaya of Setif in northern Algeria is presented in the absence and presence of line arresters and GIL arresters. The results of this paper can provide a rich and valuable theoretical reference for GIL simulation modeling and evaluation of lightning strike impact on hybrid overhead – GIL lines.

Rain may improve survival from direct lightning strikes to the human head

There is evidence that humans can survive a direct lightning strike to the head. Our question is: could water (rain) on the skin contribute to an increase in the survival rate? We measure the influence of rain during high-energy direct lightning strikes on a realistic three-compartment human head phantom. We find a lower number of perforations and eroded areas near the lightning strike impact points on the head phantom when rain was applied compared to no rain. Current amplitudes in the brain were lower with rain compared to no rain before a fully formed flashover. We conclude that rain on the scalp potentially contributes to the survival rate of 70–90% due to: (1) lower current exposition in the brain before a fully formed flashover, and (2) reduced mechanical and thermal damage.

Enhanced through-thickness electrical conductivity and lightning strike damage response of interleaved vertically aligned short carbon fiber composites

Through-thickness electrical conductivity of carbon fiber reinforced polymers (CFRPs) is a key characteristic that determines the severity of lighting strike-induced damage. Carbon Fibers (CFs) are inherently electrically conductive and therefore provide high conductivity in the direction of the fiber orientation. However, electrical conductivities through the thickness and orthogonal to the CF orientation in CFRPs are governed by the insulating polymer matrix present between CFs. In this work, through the thickness alignment of short CFs in between layers of CFRP laminates is demonstrated to improve the through-thickness electrical conductivity. Composites with interleaved vertically aligned short CF fibers (<150 μm) will be referred as V-fiber composites hereafter. The effect of the V-fiber on the lightning strike damage is evaluated against an artificial lightning strike of 100 kA (modified waveform A of SAE ARP-5412B standard). The improved through-thickness electrical conductivity of CFRP laminates (1.15 S/cm) through vertical alignment of short CFs was compared to reference CFRP laminates (0.13 S/cm) and was found to dissipate the artificial lightning strike current more efficiently. The surface damage after the artificial lightning strike in the V-fiber composites was reduced to 12.69 cm2 compared to the reference CFRP surface damage of 57.67 cm2, a 78% reduction. It was also demonstrated that Joule heat generated due to lightning strike on the composites was significantly less than the reference sample using infrared (IR) thermography. A high retention (up to 78%) of flexural properties (modulus and strength) was observed in V-fiber composites post lightning strike impact as compared to only 47% retention in the reference panel.

Performance Level and Strike Type during Ground and Pound Determine Impact Characteristics and Net Force Variability.

The evaluation of strike impact is important for optimal training, conditioning and tactical use. Therefore, the aim of this study was to evaluate ground and pound strikes, in terms of net force variability, across genders and performance levels. Eighty-one participants, professional men (n = 8, 37 ± 6 years, 195 ± 7 cm, 113 ± 27 kg), advanced men (n = 47, 26 ± 8 years, 180 ± 7 cm, 76 ± 11 kg), and advanced women (n = 26, 21 ± 1 years, 167 ± 6 cm, 61 ± 7 kg) performed three strikes from a kneeling position into a force plate on the ground. The elbow strike resulted in the highest impulse and the palm strike in the highest peak force for all three categories. These results support the recommendation that has previously been made to teach the palm strike to beginners and advanced tactical and combat athletes. The direct punch and elbow strike net force were characterized by a double peak curve, where the first peak variability explained 70.2-84% of the net force. The second peak was pronounced in professional men during elbow strikes, which explained 16% of net force variability. The strike type determines the impact net force and its characteristics, where palm strike is typical by highest peak impact tolerance and elbow strike by double force peak with high net force impulse.

Reliability and Practical Use of a Commercial Device for Measuring Punch and Kick Impact Kinetics.

Martial arts, boxing and combat sports such as mixed martial arts participation have gained popularity in recent years internationally. One common aspect to these sports is the training and skill in maximizing strike impact of punches and kicks, referred to as impact kinetics, with commercial devices now available to assess punching and kicking power in athletes training facilities and gyms. We, therefore, assessed the reliability of a commercial device, the PowerKubeTM (Strike Research Ltd., Norwich, England) via the technical error of measurement (TEM) in both linear and non-linear simulated strikes to the center of target, off-center, level and inclined in a laboratory setting. The highest mean impact power resulted from level, center strikes (5782 ± 230 W) followed by level, off-center strikes (4864 ± 119 W, p < 0.05), inclined center strikes (4500 ± 220 W, p < 0.05), and inclined, off-center strikes (3390 ± 151). Peak power reductions ranged from 15.9% (level, off-center) to a maximum of 41.4% (incline, off-center) compared to the level, center strikes. Coaches are advised to take steps such as videoing strikes with high sampling rates to better ensure consistency in impact orientation, being perpendicular and centered on the strike pad, to best capture the peak power of kicks or punches.

The effect of warm-up on peak impact force of the rear hand strike in full-contact combat sports

ABSTRACT Warming up is a generally accepted practice that leads to improved performance and reduces the risk of injury in a wide range of sports. However, the evidence about the influence of warm-up in combat sports is limited and, specifically, little is known about the impact which delays between a warm-up and the start of a match may have on fighters’ performance. This study investigates the influence of warm-up and cool-down on one of significant performance predictors in full-contact combat sports, the peak force of a rear hand strike, in a sample of 31 athletes.Peak impact force was measured before, after, and at two time points after a standardized warm-up routine; skin temperature and heart rate were also monitored. Warm-up and cool-down periods were substantial predictors of body temperature and heart rate, but we observed no effect of the warm-up routine on strike impact force. Strike impact force remained unaffected even after the cool-down intervals.Strike impact force does not seem to respond to physiological changes elicited by a warm-up. This measure is partly related only to fighters’ physical characteristics, namely the body weight. Athletes and trainers could thus concentrate on other aspects of successful performance during warm-up routines.

Numerical Analysis of Bird Impact Over the Aircraft Windshield

Bird impact on aircraft is one of the most important foreign object damages, which result in the reduction in airworthiness. Most bird impacts are not fatal but bird impact can be deadly when the impact is at engine assembly, leading-edge and Frontal area of aircraft. This study focuses on bird impact on windshield and its effects on stress concentration and energy absorption. The strength and stiffness of the windshield play a vital role during foreign object damage. Laminated glass is used as a windshield, the reason to use interlayer is to avoid separation of other layers after impact which ultimately reduces risk to pilot. Laminate configurations glass/PMMA/glass and PMMA/Polycarbonate/PMMA are used for the windshield. Impact analysis has been carried out at velocities of 50m/s, 100m/s and 150m/s. Modeling and solving are done in LS-Pre post and LS-Dyna using a FE-SPH approach. Simulations are carried out impact against bird, stress and energy absorption as the output. Based on results, PMMA/Polycarbonate/PMMA laminate is most likely to sustain the bird strike impact without failure.

Biomechanical Analysis of Running in Shoes with Different Heel-to-Toe Drops

The heel-to-toe drop of running shoes is a key parameter influencing lower extremity kinematics during running. Previous studies testing running shoes with lower or larger drops generally used minimalist or maximalist shoes, where the factors outside of the drop may lead to the observed changes in running biomechanics. Therefore, our aim was to compare the strike patterns, impact force, and lower extremity biomechanics when running in shoes that varied only in their drops. Eighteen habitual rearfoot strikers performed trials wearing running shoes with four drop conditions: 15 mm, 10 mm, 5 mm, and without a drop. Three-dimensional (3D) tracks of the reflective markers and impact force were synchronously collected using a video graphic acquisition system and two force plates. The biomechanical parameters were compared among the four drop conditions using one-way ANOVA of repeated measures. A greater foot inclination angle (p = 0.001, ηp2 = 0.36) at initial contact and a lower vertical loading rate (p = 0.002, ηp2 = 0.32) during the standing phase were found when running in shoes with large drops compared with running in shoes without a drop. Running in shoes with large drops, as opposed to without, significantly increased the peak knee extension moment (p = 0.002, ηp2 = 0.27), but decreased the peak ankle eversion moment (p = 0.001, ηp2 = 0.35). These findings suggest that the heel-to-toe drop of running shoes significantly influences the running pattern and the loading on lower extremity joints. Running shoes with large drops may be disadvantageous for runners with knee weakness and advantageous for runners with ankle weakness.

Gradient Boosting Machine to Assess the Public Protest Impact on Urban Air Quality

Political and economic protests build-up due to the financial uncertainty and inequality spreading throughout the world. In 2019, Latin America took the main stage in a wave of protests. While the social side of protests is widely explored, the focus of this study is the evolution of gaseous urban air pollutants during and after one of these events. Changes in concentrations of NO2, CO, O3 and SO2 during and after the strike, were studied in Quito, Ecuador using two approaches: (i) inter-period observational analysis; and (ii) machine learning (ML) gradient boosting machine (GBM) developed business-as-usual (BAU) comparison to the observations. During the strike, both methods showed a large reduction in the concentrations of NO2 (31.5–32.36%) and CO (15.55–19.85%) and a slight reduction for O3 and SO2. The GBM approach showed an exclusive potential, especially for a lengthier period of predictions, to estimate strike impact on air quality even after the strike was over. This advocates for the use of machine learning techniques to estimate an extended effect of changes in human activities on urban gaseous pollution.

Dissecting lightning strike hazard impact patterns to National Airspace System facilities in the contiguous United States

Lightning strikes pose a severe threat to the United States (US) National Airspace System (NAS). Although the US Federal Aviation Administration (FAA) implements lightning protection practices and procedures to protect personnel, electronic equipment, and structures within the NAS, many lightning-induced outages still occur. To date we found that most research on lightning-induced facility outages has focused on understanding the physical processes of lightning strike effects on aircraft and airport ramp operations. Very little research has been done on examining the overall patterns and characteristics of such hazards to aviation from a geo-spatial standpoint. To bridge this gap, we analyze nationwide lightning strike spatiotemporal data and FAA airport facility outage records from 2009 through 2020 and apply innovative pattern recognition methods to identify key characteristics of lightning strike hazards. Our results uncover the complexities of lightning strike hazard impact patterns to NAS facilities, identifying five distinct typologies with climatological signatures critical to creating better hazard mitigation strategies.

Numerical Modelling of Bird Strike on Aerospace Structures by means of Coupling FE-SPH

This article offers a parametric mechanics investigation in defining the correlation between the parameters of a wing-body during a bird strike collision. A commercial software of LS-Dyna is used to compute the numerical modelling manifested in this research. In this study, it is an attempt to form a definitive work based on the Smoothed Particle Hydrodynamics (SPH)formulation by recognising the most critical influencing parameters in the bird-strike computation and verify the simulation with the experiment data. For instance, an idealised bird is modelled as a cylindrical shape with hemispherical ends to maintain the homogeneity and symmetryusing SPH approach. Moreover, an aluminium alloyrigid flatplate is modelled as a shell element plate in the finite element model (FEM). Here, internal energy vs time for different plate thickness graph are plotted to observe the difference of absorbed energy during the impact. Such conditions are considered in this research from the sight of bird strike impact under multiple states (structural thickness) and constraints (bird size). The obtained computational results are in adjacent agreement with the experimental results published in another literature.

Equivalent mechanical load model methodology to simulate lightning strike impact on protected and painted composite structure

Lightning strike damage on aircraft composite structure is very difficult to predict. The main source of this damage is the mechanical constraint generated by the lightning in interaction with the structure made of composite, protected with a metallic mesh and painted. The purpose of this paper is to propose a numerical model able to reproduce the surface overpressure generated by the explosion of the lightning strike protection (LSP) and its confinement with the paint. Comparisons of numerical displacements with lightning experimental ones are presented in order to analyse the predictability of the model. This is a first step in order to assess the damage in the composite structure depending on the design configurations (CFRP, LSP and Paint) when combined with a damage model.

Creation of a prototype biomimetic fish to better understand impact trauma caused by hydropower turbine blade strikes

Biomimetic model organisms could be useful surrogates for live animals in many applications if the models have sufficient biofidelity. One such application is for use in field and laboratory tests of fish mortality associated with passage through hydropower turbines. Laboratory trials suggest that blade strikes are especially injurious and often causes mortality when fish are struck by thinner blades moving at higher velocities. Dose-response relationships have been created from these data, but the exact relationship between fish mortality and the actual forces enacted on fish during simulated blade strike testing remains unknown. Here, we describe the methods used to create a prototype biomimetic model fish composed of ballistic gelatin and covered with a surrogate skin to better approximate the biomechanical properties of a fish body. Frozen fish were scanned with high-fidelity laser scanners, and a 3D-printed, reusable mold was created from which to cast our gelatin model. Computed tomography scan data, imaged directly or taken from online data repositories, were also successfully used to create CAD models for use in additive manufacturing of molds. One 3-axis accelerometer was embedded into the gelatin to compare accelerometer data to dose-response data from previous laboratory research on live fish. The resulting model (i.e., Gelfish) had a statistically indistinguishable tissue durometer to that of real fish tissue and preliminary blade strike impact testing suggested its overall flexibility was similar to that of live fish. Gelfish was designed with biofidelity as its guiding principle and our results suggest initial experimentation was successful. Future research will include replication of initial Gelfish test results, quantitative measurement of model flexibility relative to real fish, and inclusion of surrogate skeletal structures to enhance biofidelity. Use of more sophisticated sensors would also better quantify the physical forces of blade strike impact and help determine how said forces correlate with rates of mortality observed during tests on live fish.

Design and Optimization of Hybrid Interface Joint in a Composite Fan Blade of Aircraft Engine

Fan blades are one of the most important components of an aircraft engine. Bird strikes on fan blades have always been a cause of worry and it can cause slices of birds hitting other parts of the engine which may lead to greater damages. Bird strikes cannot be completely avoided. However, reduction of the impact of a bird on jet engines can be achieved by suitable design and manufacturing, through the simulation analysis. Although current composite blades can withstand the bird strike impact, some delamination failures are still observed on the trailing edge side of the blade, possibly due to vibration bending modes This paper talks about using two fibers in composite blade instead of the current single fiber one. For this to be feasible, two fiber joints at various locations on the blade have to be properly designed. The design criteria used here is the lowest inter-laminar shear strain level at critical joint locations. Suitable size coupon models in FEA with hybrid joints inside are used to simulate the blade bending with appropriate boundary conditions. The coupon models were developed by using the ANSYS APDL and linear static analysis was performed for different repetitive layups and varying layer by layer joint locations. The coupon joint designs with minimum inter-laminar shear strains are shortlisted to be recommended for use in sub-element and blade models.

Numerical Investigation on the Damage of Whirling Engine Blades Subjected to Bird Strike Impact

This research renders a numerical investigation of whirling engine blades subjected to bird strike impact. The numerical modelling of the bird strike investigation was conducted employing SPH. The bird model was established as a gelatine material and is the geometry of the bird was anticipated. As most bird strikes transpire during take-off and landing, the bird was modelled with a set velocity of 120m/s and is impacted on the engine blades, where the damage of the blades is then assessed. The engine blades were modelled as a tetrahedron mesh for accuracy in LS-DYNA software and are rotating at 200 rad/s counter-clockwise. The engine blade material is modelled with Johnson-Cook failure constants. The results are manifested as effective stresses, which shows the structural damage of the engine blades struck by the bird, which induces deflection that significantly damages the blades. Further assessments of bird velocity and engine blade rotation variations are also presented.

Verification Protocols for the Lightning Protection of a Large Scale Scientific Instrument in Harsh Environments: A Case Study

This paper is devoted to the study of the most suitable protocols needed to verify the lightning protection and ground resistance quality in a large-scale scientific facility located on a site with high risk of lightning strikes. We illustrate this work by reviewing a case study: the largest telescopes of the Northern Hemisphere Cherenkov Telescope Array, CTA-N. This array hosts sensitive and high-speed optoelectronics instrumentation and sits on a clear, free from obstacle terrain at around 2400 m above sea level. The site offers a top-quality sky but also features challenging conditions for a lightning protection system: the terrain is volcanic and has electrical resistivities well above 1 kOhm·m. In addition, the environment often exhibits humidities well below 5%, and strong winds pose challenging conditions. On the other hand, the high complexity of a Cherenkov telescope structure does not allow a straightforward application of lightning protection standards. We describe here how the risk assessment of direct strike impacts was made and how contact voltages and ground system were both tested. Finite Element Simulation (COMSOL Multiphysics) has been used to estimate the current flowing through the parts of the earthing system designed for the telescopes in the case of a direct strike impact. This work is intended to provide assistance to scientists and managers involved in the construction of scientific installations, particularly those in charge of defining verifiable reliability and safety requirements for lightning protection.

Performance comparison of resin-infused thermoplastic and thermoset 3D fabric composites under impact loading

In this paper, the impact performance of a novel resin-infused acrylic thermoplastic matrix-based 3D glass fabric composite (3D-FRC) has been evaluated and compared with thermoset based 3D-FRC under single as well as recurring strike low velocity impact (LVI) events. The single impact tests revealed that the thermoplastic-based 3D-FRC exhibits up to 45% reduced damage area and can have up to 20% higher impact load-bearing capacity (peak force). The damage mode characterization showed that damage transition energy required for micro to macro damage transition is 27% higher, and back face damage extension is up to 3 times less for thermoplastic-based 3D-FRC. Meanwhile, the recurring strike impact test highlights that the thermoplastic-based 3D-FRC experiences a 50% less damaged area, better structural integrity, and survived more strikes. The comparison of single and repeated LVI tests have also allowed us to present a design criterion for estimating the safe number of repeated LVI events for a given impact energy. The superior impact resistance of thermoplastic-based 3D-FRC is attributed to their higher interlaminar fracture toughness, a tougher fiber-matrix interface, matrix ductility, and unique failure mechanism of yarn straining, which is not present in thermoset composites.